Extrusion die



Oct. 6, 1964 v. E. SENEGAL I 3,

EXTRUSION DIE Filed Aug. 2, 1961 2 Sheets-Sheet 1 INVENTOR VANCE EVAN SENECAL BY UM M ATTORNEY Oct. 6, 1964 v. E. SENEGAL 3,151,356

EXTRUSION DIE Filed Aug. 2, 1961 2 Sheets-Sheet 2 M INVENTOR y VANCE EVAN SENEGAL ATTORNEY United States Patent 3,151,356 EXTRUSION DIE Vance Evan Senecal, Wilmington, Del., assignor to E. I. do Pout de Nemours and Company, Wilmington, Deb, a corporation of Delaware Filed Aug. 2, 1961, Ser. No. 128,775 9 Claims. (Cl. 18-12) This invention relates to an extrusion coating die for applying a coating to a moving web. Photographic films and papers usually comprise a sheet support and a multiplicity of layers. In the case of black and white films not as many layers are required as for multicolor films. In the former films, however, it is common practice to coat a gelatino-silver emulsion onto a film base and then to coat the emulsion layer with a non-photographic aqueous gelatin solution to provide an antiabrasion layer. In color films, there is usually a separate layer for recording each of the primary colors, and yielding a dye image in addition to filter and antiabrasion layers. All of the above layers are usually formed by separate coating operations. The various layers in these multilayer photographic elements, particularly in the case of color films, should be of uniform thickness and free from defects.

In black and white films the variation in coating weight, ideally, should not exceed i2.0%, and in multicolor films, i0.5%. In order to coat a highly viscous photographic emulsion having a low fluid content at high speeds, emulsions are extruded through a die at high pressures, i.e., greater than 100 pounds per square inch. Dies suitable for this purpose usually comprise an internal supply chamber and an orifice formed by two lips coextensive with said chamber. In order to deposit the desired amount of emulsion per unit of surface at coating speeds of 80 to 400 feet per minute, the orifice must be precisely adjusted and the lips rigid so that the width of the orifice through out its entire length can be maintained within precise narrow limits. This is because for ideal or so-called Newtonian fluids the coating weight varies as the third power of the width between the lips.

Since fluid photographic emulsions are non-Newtonian in character, the coating weight of the emulsion layer may vary as much as the 4th or 5th power of the gap or width dimension variation between the die lips. It has been found that, even where the die and lips are rigid, it is diflicult to maintain the transverse coating weight uniform within the above limits. This is due to the deflection of the die lips during the high pressure extrusion thereby giving a non-uniform coating weight profile.

Various types of dies have been proposed in order to provide uniform coatings but uniform flow distribution throughout dies of considerable length is difficult to attain and improper distribution causes defects in the form of streaks.

An object of this invention is to provide an improved extrusion die. A further object is to provide an extrusion die which will give a uniform coating under conditions of high fluid pressures. Another object is to provide such a die which will give smooth, uniform, wide coatings devoid of streaks and other coating defects. A further object is to provide a simple and dependable extrusion die. A further object is to provide a die having improved flow distribution. A still further object is to provide a simple, internally-braced die that can be readily assembled and is useful in applying one coating or two coatings inlet for fluid material, a coacting plate on each surfacesimultaneously to a web. Still other objects will be ap- Patented Get. 6,1964

tear-drop in design, and small in Width, the space between adjacent braces being of greater width. In the preferred extrusion die, there is also a row of spaced streamline braces in the transverse restricted passage. These are shown on one plate in the drawings.

If desired, each plate can be provided with a pressure measuring and controlling device mounted adjacent to and in communication with the fluid supply chamber. Also, if desired, the body and/ or plate can be provided with passages and fittings so that a heat-exchange fluid can be circulated therethrough to control the temperature of the body or plate.

The invention will now be described with reference to the accompanying drawings in which:

FIG. lis a vertical cross-section of the extrusion die adjacent to a coating roller and web to be coated, and

FIG. 2 is a plan view of one of the plate members showing the location of the flow distribution chambers or cavities and the location of the internal braces in relation to the lips of the die.

Referring now to the drawings wherein the same reference numerals refer to the same parts in the several views, the extrusion die of this invention comprises a wedge-shaped central body member 1 having in each slanting side surface 2 a transverse recessed fluid supply chamher 3 and an inlet passage 4 connecting said chamber to a source of supply of fluid material. Each side surface of the body member has attached thereto a fluid distributionand orifice-defining plate 5.

In the inner surface of each plate, opposite the supply chamber, is a coextensive recessed supply compartment 6. Spaced therefrom is a second transverse recessed fluid distribution compartment '7, the bottom wall 8 of which I slopes inwardly toward the coacting slanting surface until it meets a slot orifice-defining surface 9 which is preferably parallel to said surface for a short distance.

Between the supply chamber and the fluid distribution chamber formed by the compartment and the plate there is a restricted fluid distribution passage 10 of less depth than either of said chambers. The passage may be of uniform width throughout its transverse length or wider near the source (e.g., 4) of fluid and vary progressively to a narrower width more distant from said source. The leading and/or trailing edge of the passage can vary as shown in dashed lines in FIG. 2. A transverse row of spaced streamline braces 11 of small width can be disposed in the restricted passage. These braces are essentially the same in height as the depth of the passage. In the fluid distribution chamber, there isa second transverse row of spaced braces 12 of the same type but of greater height so as to fill the space between the slanting surface and the inner surface of said fluid distribution chamber. The braces, in general, are spaced apart a distance at least twice their width and preferably they are spaced from the end wall of their respective chambers an equal distance. The two rows of braces, moreover, should be placed so that the braces in one row are not in axial alignment with those in the other row but preferably are midway between the spacings in the other row.

. into surface contact.

or withdrawn from, engagement with the coacting part of the body.

In addition to the fastening screws 16 the plates are -fastened to the body member by a plurality of bolts 18 which are spaced near the sides and across the tops of the plates, as shown in FIG. 2 of the drawings. If desired, these bolts can be countersunk into the plates.

If the braces 12 are not integral with the plates or welded thereto, they are preferably fixed in position by means of small screws 19 passing through interfitting holes in the braces and threadably engaging coacting threads in the inner surface of the plate. If desired, the braces can be fastened to the body member by any suitable means.

Each plate is preferably provided with a lateral socket 20 opposite the fluid supply chamber and having communication therewith through passages 21. A pressuresensitive device, e.g., a pressure transducer 22, is placed in the socket and is fixed in place by a suitable guide sleeve 23 and held in place by a suitable cap 24, the sleeve and cap being held in place by meansof screws 25 and 26. A lateral pipe 27 extends through the cap and is connected to the transducer. The pipe connects with a suitable control device so that the fluid pressure in the fluid supply chamber can be controlled and determined.

Coacting with each fluid inlet passage 4 there is a pipe sealing flange 28 which is fastened to the upper surface of the body member. Pipe 29 fitted into the flange connects to a source of fluid material to be extruded. The source for one supply chamber can be different from that of the other chamber.

While not shown in the drawings, the body member and/ or each plate or both plates can be provided with channels or passages for the circulation of a heat-exchange li uid.

As shown in FIG. '1 of the drawing, the bottom edge of each plate preferably meet at or near the apex of the body member so that the sheets of material being extruded meet at the orifice. In this way a composite sheet can be formed from the two extruded layers as they come The bottom of each of the plates can be of the same pointed shape or they can be different, as shown in FIG. 1 of the drawings.

The wedge shaped body may come to a knife-edge or sharp point or it may be truncated slightly to form, for example, a flat edge, e.g., about 1 to /s inch in width.

In assembling the device, the internal braces, which are carefully machined and lapped to an accuracy of :20 microinches to provide the proper orifice dimensions, are fastened in their respective positions by screws 19. The plate members are then put in place and fastened down with the screws 16 and bolts 18, some of which pass through the internal braces. Gaskets or shims may be inserted around the periphery or outside edges to seal the chambers. By varying the height of the braces or by adding similarly shaped shims, the height of the restricted passage and chambers as well as the width of the fluid orifice can be adjusted. Stocks of separate braces of different height can be maintained so that the apparatus can be readily reassembled for extrusion of different material.

The plate members and wedge-shaped member can be made of any strong metal or metal alloy. The plate memher and wedge-shaped member, for example, can be made of cast iron, stainless steel, die steel, including vanadium steel, titanium, brass or bronze. For example, when coating a photographic emulsion with a l2-mil lip opening to control coating weights within :0.5% across the web, all interior surfaces including mating surfaces and the die lips must be highly polished to within a dimensional accuracy :20 microinches. The particular metal used be ust as easily be used to coat single layer products.

will depend on the corrosive characteristics of the material being coated. The various screws, bolts, etc. can be made of steel, stainless steel, titanium or other suitable metal or metal alloy.

In operation, when coating, for example, a viscous, aqueous photographic silver halide gelatin emulsion and an aqueous gelatin solution to form an antiabrasion layer, the extrusion coating die is placed in position for coating a suitable web. In FIG. 1, the extrusion coating die is shown in position relative to the coating roll supporting the web to be coated. In normal coating position, the center line of the emulsion flow path should be directed up at an angle of 35 to the horizontal and approximately tangent to the coating roll surface. The length of the unsupported region of flow for the composite sheet of silver halide emulsion layer and antiabrasion layer where it is being drawn down from the plane of the tips of the lips on the plate members 5 to the point of contact with the web on the coating roll should not exceed 0.300 inch in the direction of web travel. In the arrangement, a continuous sheet of film or paper 30 from a source (not shown) passes around a support roller 31 and to a suitable drying zone and thence to a windup apparatus (all not shown).

In using the extrusion die of this invention, two thin wide layers of viscous material are simultaneously extruded under pressure and brought into surface contact at or near the orifice, then applies to the surface of a continuous web moving at a speed greater than the speed of extrusion. The layers, as they leave the orifice, can be about 0.25 to 12 mils in thickness and when one layer is used as a sublayer or protective layer for the main layer, in general, it will be to /2 the thickness of the layer of a desired coating material may also be coated by using only one side of the novel coating die.

The extrusion die of the invention is particularly useful in simultaneously extruding (a) a thin layer of an aqueous dispersion of light-sensitive silver halide in a natural or synthetic water-permeable colloid and (b) a thin protective layer of a water-permeable colloid containing an antistatic agent, or (c) an antihalation layer from an aqueous dispersion or solution of-an antihalation pigment or dye in a water-permeable colloid binding agent and then applying the composite layer to the surface of a moving web of film or paper. Alternatively, two different aqueous dispersions of silver halide in a water-permeable macromolecular organic colloid can be extruded simultaneously and the composite layer coated onto a continuous moving web. The above two different dispersions may contain color formers or filter dyes and .may be two of the record and/or auxiliary layers of a multilayer film for color photography. An important feature of .the invention is that the novel coating die can In an exemplary procedure of coating a single layer, a silver halide emulsion was made, extruded and coated onto a cellulose acetate film base as follows:

A dilute aqueous emulsion containing about 5.9% silver halide and about 10.0% gelatin, by weight, was concentrated to about 50 to 52% solids content and the temperature adjusted to about P. where the viscosity was about 5000-6000 centipoises. The silver halide emulsion coating solution was fed from a pressurized chamber into one inlet passage 4 of the dual extrusion coating die 4 of this invention. The flow rate was adjusted so that the emulsion was applied at the rate of approximately 65 mg. silver halide per square decimeter. V

The die lips were placed above a fii-inch diameter coating roll so that the draw-down span between the web and the bottom edge of the plate on the left side was 0.150 inch. The pressure in the coating chamber was held at 45 mm. mercury absoluteand the coating speed was 235 feet per minute. After coating, the film was dried by means of infrared heaters and had satisfactory photographic quality. The film had good adherence to the base and the layer was uniform in thickness throughout its area indicating auniform transverse coating weight profile across the width of the web.

In an exemplary procedure of coating two layers of a color film, a cyan color forming emulsion and a gelatin separator layer were made, extruded simultaneously and coated onto a cellulose acetate film base in the following manner:

A dilute aqueous emulsion containing about 2.2% silver halide, 2.4% gelatin, and a cyan color former was concentrated to about 34%, by weight, solids content and the temperature adjusted to about 110 P. where the viscosity was about 53 00 centipoises. A separation layer coating solution containing about gelatin and a small amount of hardening agent Was concentrated to 36%, by weight, solids at 110 P. where the viscosity was about 3500 cp.

The silver halide emulsion and separation coating solution were fed from pressurized chambers into the respective inlet passages in the dual extrusion die as shown in the drawings. The flow rates were adjusted individually so that the emulsion was applied at the rate of approximately 35 mg. silver halide per sq. dm. and the separator coating at about mg. gelatin per sq. dm. The die lips were placed above a one-half inch diameter coating roll so that the draw-down span was 0.150 inch. The pressure in the coating chamber was held at 45 to 60 mm. mercury absolute for film coating speeds ranging from 60 to 200 feet per minute. The film was dried by means of infrared heaters and had good photographic quality. It was suitable for coating the succeeding layers of the color film. The composite film had good adherence to the base support and the layers were uniform in thickness throughout their areas indicating uniform transverse coating weight profiles across the width of the web.

Various kinds of liquid or liquefied materials can be extruded by the apparatus of this invention. Among such materials are film-forming polymers including polyethylene, polyvinyl chloride, poly(viny1 chloride co vinyl acetate), polymethyl methacrylate, polystyrene, polyethylene terephthalate; regenerated cellulose, cellulose acetate, cellulose propionate, cellulose acetate butyrate and ethyl cellulose; rubber hydrochloride, etc. These materials can be extruded in the form of an aqueous dispersion, solution in a solvent, or in molten or liquified form. The apparatus is especially useful in coating gelatino-silver halide emulsions, and other dispersions of finely divided materials in water-permeable colloids.

When the material being extruded has to be held at a certain temperature, a heat-exchange fluid, e.g., water, diphenyl oxide, chlorinated biphenyl, chlorinated naphthalene and parafiin hydrocarbon oils maintained at the requisite temperature, is passed through the circulation passages in the wedge-shaped member and the plate mem bers.

Antiabrasion coatings, such as those used to coat X-ray sensitive silver halide emulsions are effective in thicknesses as low as thirty millionths of an inch. Yet, such exceedingly thin layers are difiicult to extrude or coat in the form of uniform wide layers. By using the extrusion die of this invention, such exceedingly thin layers can be readily extruded and coated onto webs over long periods of time. By extruding one extremely thin silver halide emulsion layer in contact with a thick emulsion layer, the composite films or layers can be stretched during the coating operation, whereas the extremely thin layer would be too fragile to be stretched or drawn down separately.

The apparatus of this invention has'the advantage that it is simple in design but dependable in operation. It enables one to extrude a composition onto a rapidly moving web with uniform distribution throughout the thickness and width of the layer and without coating streaks. A

further advantage of the invention is that the apparatus enables one to provide an extruded composite film having a uniform coating weight profile across the width of the coating or layer. A still further advantage of the die of this invention is that it has a few simple parts which can be readily assembled and quickly adjusted to give a coating of uniform profile.

The photographic films and papers obtainable by use of the extrusion die of the invention, moreover, have improved characteristics. Multilayer color films having extremely thin filter, light-absorbing barrier and other layers contiguous with or adjacent to a silver halide emulsion layer or layers, antihalation layers, etc. have improved resolution over films having thicker layers obtainable by conventional coating methods.

What is claimed is:

1. An extrusion die comprising (1) an elongated wedge-shaped body having a transverse fiuid supply compartment in each slanting surface of the body which compartment communicates with an inlet for fluid material,

(2) a coacting plate on each said surface forming with said compartment a fluid supply chamber and with the bottom edge of said surface a long, narrow extrusion orifice,

(3) a transverse recessed fluid distribution chamber located between the wedge-shaped body and the coacting plate and of lesser depth than said supply chamber, said distribution chamber being located between said supply chamber and said orifice and communicating with said orifice, and

(4) a transverse restricted passage communicating between the two chambers and essentially the same length as said chambers.

2. An extrusion die comprising (1) an elongated wedge-shaped body having a fluid supply compartment in each slanting surface of the body and communicating with an inlet for fluid material,

(2) a coacting plate on each said surface forming with said compartment a fluid supply chamber and with the bottom edge of said surface a long, narrow extrusion orifice,

(3) a transverse recessed fluid distribution chamber of lesser depth than said supply chamber and located in the inner surface of said plate said fluid distribution chamber being between the wedge-shaped body and the coacting plate and also between said supply chamber and said orifice and communicating with the orifice,

(4) a transverse restricted passage communicating between the two chambers and essentially the same length as said chambers, and

(5) a row of streamline braces in the fluid distribution chamber.

3. An extrusion die according to claim 2 wherein there is a row of streamline braces in the transverse restricted passage.

4. A die according to claim 2 wherein there are streamline braces in the transverse restricted passage, there being holes in the braces and coacting holes in said plate and body for the reception of adjustable fastening elements.

5. A die according to claim 2 wherein the braces are integral with the plate.

6. A die according to claim 2 wherein the braces are separate parts and are provided with holes and screws for fastening them to the plate.

7. A die according to claim 2 having a pressure regulating device in each plate communicating with a source of fluid pressure and with the fluid supply chamber.

8. A die according to claim wherein the lower part of the plate is parallel to the surface of the body for a short distance.

9. A die according to claim 2 wherein the lower part of the plate is parallel to the surface of the body for a short distance and the bottom wall of the fluid distribution chamber slopes inwardly until it meets said parallel part.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Canada Mar. 

1. AN EXTRUSION DIE COMPRISING (1) AN ELONGATED WEDGE-SHAPED BODY HAVING A TRANSVERSE FLUID SUPPLY COMPARTMENT IN EACH SLANTING SURFACE OF THE BODY WHICH COMPARTMENT COMMUNICATES WITH AN INLET FOR FLUID MATERIAL, (2) A COACTING PLATE ON EACH SAID SURFACE FORMING WITH SAID COMPARTMENT A FLUID SUPPLY CHAMBER AND WITH THE BOTTOM EDGE OF SAID SURFACE A LONG, NARROW EXTRUSION ORIFICE, (3) A TRANSVERSE RECESSED FLUID DISTRIBUTION CHAMBER LOCATED BETWEEN THE WEDGE-SHAPED BODY AND THE COACTING PLATE AND A LESSER DEPTH THAN SAID SUPPLY CHAMBER, SAID DISTRIBUTION CHAMBER BEING LOCATED BETWEEN SAID SUPPLY CHAMBER AND SAID ORIFICE AND COMMUNICATING WITH SAID ORIFICE, AND (4) A TRANSVERSE RESTRICTED PASSAGE COMMUNICATING BETWEEN THE TWO CHAMBERS AND ESSENTIALLY THE SAME LENGTH AS SAID CHAMBERS. 